This study seeks to evaluate a food frequency questionnaire for use in retrospective studies of dietary intake in cancer prevention research. Measures of dietary selenium, retinol, carotenes, and alpha-tocopherol will be compared with measures of serum levels of these nutrients. Intake will be measured by a food frequency questionnaire developed by the Cancer Prevention Research Unit (CPRU) at the Fred Hutchinson Cancer Research Center (FHCRC). An attempt will be made to contact and administer the questionnaire to cancer cases and controls identified in a CPRU-funded study of serum nutrients and subsequent cancer risk. That study has identified 199 cancer cases, and 398 matched controls selected from the noncases, from two employee groups from whom blood samples were drawn and frozen in 1972-76. For this study, an attempt will be made to interview the 130 living cases and a sample of living controls (n=210) matched on age, sex, race, and year and season of blood draw. These persons will be interviewed by telephone to obtain demograhic data and information on major factors other than dietary intake which may influence serum levels of these nutrients. Nutrient intake data will be obtained using a mailed food frequency questionnaire which will ask for usual serving sizes and frequency of consumption of slected foods and food groups. The validity of the nutrient intake measures will be assessed by analyzing the association between serum nutrient levels (measured as part of the CPRU-funded study) and computed estimates of nutrient intake based on the food frequency questionnaire. The CPRU food frequency questionnaire is similar to others in the field that have been and will continue to be used in epidemiologic studies, both in terms of the food items included and the retrospective orientation appropriate for case-control studies. Thus, the study has the potential to provide valuable methodologic information on the validity of retrospective food frequency techniques which are used in hypothesis generation for cancer prevention interventions.